Animals age physiologically as their biological systems deteriorate through cross-linkages, oxidation of free radicals, and other biochemical anomalies. Both intrinsic (genetic) and extrinsic (stress, temperature, and nutrition) factors affect the rate of this physiological aging process. Lipofuscin age pigments, complexes of lip-proteins found in cellular cytoplasm, exist in many phyla of organisms, and are considered to be the most universal and clearly discernible indicators of aging in post- mitotic cells. Since these compounds of metabolic waste are considered by most researchers to be non-degradable through normal intracellular enzymatic processes, and that the rate of accumulation of lipofuscin peroxidation products in cells has been shown to be directly related to the metabolic rate of the organism, studies of lipofuscin accumulation may be utilized in defining the state of an organism's physiological age. This study will examine the occurrence and accumulation of lipofuscin pigments in the brain tissues of the tropical damselfish, Dascyllus albisella; the antarctic icefish Chamsocephalus gunnari; and the antarctic codfish Notothenia rossii, an will determine the relationship between brain lipofuscin levels and chronological age as determined by examination of otoliths. Studies of lipofuscin accumulation in the brain tissues of fish will enable us to address a number of basic questions in regards to organizational aging and growth rates and the effects of various ecological parameters on the process of aging or the organismal 'rate of living'.